VMware Fusion (for Mac)

Pros

Runs Windows and other operating systems on the OS X desktop.
Tight integration of Windows apps with OS X.
Low-clutter, customizable integration between Windows and OS X.
Works well with legacy applications under Windows XP.
Simple setup.

Cons

Very slightly slower than Parallels Desktop in some functions.

Bottom Line

One of two superb OS X apps (the other is Parallels Desktop) that let you run Windows or Linux in tight integration with OS X itself.